How do I change back what a .dat file opens with?

I am not a systems guy by any means.  I've been trying to get the snipping tool installed on my XP system by following the directions below but have made a HUGE mistake I think.

I changed the file SnipTool.dat to .exe I also changed what it opened with by right clicking on the renamed sniptool.exe and selecting the isxunpack.exe program (the file still showed as a .dat file only renamed .exe).  

I knew I screwed up when I noticed that all my .dat files changed to the isxunpack.exe icon.  Things are still working right now but I'm afraid to reboot the machine.

How can I get the .dat files to not open with the isxunpack.exe program and instead function normally.

The directions I was following are below.

Thanks

Update (2009-07-12): Download links for isxunpack.exe and i6comp.exe added.

Microsoft’s new Snipping Tool in Windows Vista and higher makes it easier to take screenshots of pictures than having to do Print Screen. There is a backport of this tools called Snipping Tool, but it will only install if it thinks you are running on a Tablet PC. It is part of the Microsoft Experience Pack for Tablet PC package which also features the Royale theme. However, it will only install on a tablet PC and on nothing else. Here is how to extract and run it on a regular PC.

Requirements

WinRAR
i6comp.exe
isxunpack.exe
Instructions

Download Microsoft Experience Pack for Tablet PCs.
Attempt to run it and you should receive an error message  about how it can only run on tablet PCs.
Extract the .msi file from the installer by right clicking and selecting “Extract to InstallExperiencePack\“.
Open a command line and navigate to the newly created directory and type in “msiexec /a Launcher.msi“.
A window should pop up. Click next and specify a temporary directory.
After files have been extracted, open the directory in Explorer and navigate to the “Microsoft\Experience Pack\Data” sub-directory.
Rename SnipTool.dat to SnipTool.exe.
Open a command line and navigate to the directory and copy isxunpack.exe into it.
Run “isxunpack SnipTool.exe” in the command line.
Browse to the new sub-directory “Disk1“.
Open a command line and navigate to the new directory and copy i6comp.exe into it.
Run “i6comp.exe e data1.cab” and ignore the errors.
In the Disk1 directory, look at the file SnippingTool.exe and run the file.
Note that the tool will not run on nLited Windows installs without IE/WMP